Method for manufacturing a thin film semiconductor device, method for manufacturing a display device, method for manufacturing a thin film transistors, and method for forming a semiconductor thin film

ABSTRACT

For manufacturing a thin film semiconductor device, first conducted is a film-making step to make a non-single-crystalline semiconductor thin film ( 4 ) on an insulating substrate ( 1 ). Next conducted is an annealing step to irradiate laser light ( 50 ) for once heating and melting the non-single-crystalline semiconductor thin film ( 4 ) and then changing it into a polycrystal in its cooling process. Thereafter, a processing step is conducted to form thin film transistors in an integrated form, which includes the polycrystalline semiconductor thin film ( 4 ) as their active layer. For the purpose of ensuring uniform crystallization and enlargement of grain sizes, in the annealing step, by using a laser oscillator ( 51 ) including an excimer laser source, the laser light ( 50 ) having a pulse width not shorter than 50 ns is shaped by an optical system ( 53 ) to form a rectangular cross-sectional area whose sides are not shorter than 10 mm to sequentially irradiate the semiconductor thin film ( 4 ).

DESCRIPTION

Method for manufacturing a thin film semiconductor device, method formanufacturing a display device, method for manufacturing thin filmtransistors, and method for forming a semiconductor thin film.

TECHNICAL FIELD

This invention relates to a method for manufacturing thin filmsemiconductor devices involving thin film transistors formed in anactive matrix type display device in an integrated form. Moreparticularly, the invention relates to a method for formingpolycrystalline semiconductor thin film transistors.

BACKGROUND ART

Crystallization annealing by laser light has been developed as a part oftechnologies to proceed with the manufacturing process of thin filmsemiconductor devices under low temperatures. This technique firstirradiates laser light onto a semiconductor thin film of anon-single-crystalline material such as amorphous silicon orpolycrystalline silicon with a relatively small grain size, which isformed on an insulating substrate, to locally heat it, and then makesthe semiconductor film change into a polycrystal with a relatively largegrain size during its cooling process (crystallization). Thecrystallized semiconductor thin film is used as an active layer (channelregion) to integrally build thin film transistors. By employing thiscrystallization annealing, thin film semiconductor devices can be madeunder low process temperatures, and this enables the use of inexpensiveglass substrates instead of expensive quartz substrates with a higherheat resistivity.

In crystallization annealing, line-shaped laser light normally elongatedin the scanning direction is intermittently irradiated while making itsshots partly overlapped. By overlapping shots of the laser light, thesemiconductor thin film can be crystallized more uniformly.Crystallization annealing which uses line-shaped laser light (line beam)is schematically shown in FIG. 1. Laser light 50 shaped into a lineextending in the Y direction of an insulating substrate 1 of glass, forexample, is irradiated onto the surface of the insulating substrate 1having formed a semiconductor thin film. In this process, the insulatingfilm substrate 1 is moved in the X direction relative to the irradiatedregion. In this example, a line beam 50 released from an excimer lasersource is irradiated intermittently in a partly overlapped fashion. Thatis, the insulating substrate 0 is scanned in the X direction relative tothe line beam 50 through a stage. Crystallization annealing is conductedby moving the stage after each shot by a pitch smaller than the width ofthe line beam 50 to ensure that the line beam 50 can irradiate theentire surface of the insulating substrate 1. Excimer laser sources usedin conventional crystallization annealing release pulses of 100 Hz orhigher frequency, and the pulse width of each line beam is smaller than50 ns.

Thin film semiconductor devices integrating thin film transistors areused in many active matrix type display devices, or the like. In orderto realize display devices excellent in image quality, it is importantto integrate thin film transistors having good operation properties allover the substrate. For this purpose, it is necessary to uniformly stacka semiconductor thin film of a polycrystal with a relatively large grainsize. Additionally, needless to say, when taking the production yieldinto consideration, crystal grains having a large grain size must beuniformly built in all over the substrate. There are some methods forobtaining such a polycrystal, such as increasing the laser lightirradiation energy, increasing the number of shots of overlappingirradiation, and making a crystal core in an amorphous semiconductorthin film before irradiation of laser light, for example. Even withthese methods, however, no techniques have been successful in makingsufficiently large, uniform crystal grains. Therefore, nosystem-on-panels remarked as the final target of low-temperature-processhave been realized heretofore. A system-on-panel pertains to a deviceincluding built-in peripheral devices such as a video driver and atiming generator on a common substrate in addition to a switchingelement for driving pixels and thin film transistors used as horizontalscanners and vertical scanners. For realizing a system-on-panel,mobility u of individual thin film transistors has to be increased to 80cm²/V·s through 300 cm²/V·s. For this purpose, it is necessary tofurther decrease the grain size of polycrystalline semiconductor thinfilm.

As shown in FIG. 1, when the line beam is irradiated to partly overlapbetween one shot and another, streaks appear to extend in the direction(Y direction) normal to the forward direction (X direction). In amicroscopic view, these streaks are unevenness in crystal grain size.When the thin film transistors are integrated on the insulatingsubstrate, unevenness in crystal grain size is observed as unevenness ofthe operation property, and it is therefore difficult to fabricate adisplay device ensuring a high quality throughout the entire surface ofthe insulating substrate. The first object of the invention is directedto solution of these problems of conventional techniques and provides amethod for obtaining a polycrystal having a uniform, large grain sizeall over the surface of the insulating substrate by irradiating laserlight onto a semiconductor thin film.

Next explained is another problem the invention intends to overcome.Thin film transistors are widely used as switching elements of activematrix type display devices. Especially as the semiconductor thin filmto form the active layer of thin film transistors, polycrystallinesilicon has been used for years. Polycrystalline silicon thin filmtransistors are used not only as switching elements, but they can beused also as circuit elements, and peripheral driving circuits can bebuilt in together with pixel-driving switching elements on a commonsubstrate. However, to form these peripheral driving circuits,high-performance thin film transistors are required. Particularly, theirmobility is desired to be high.

Solid phase growth has been known for years as a technique for makinghigh-quality polycrystalline silicon on an insulating substrate. This isa method which makes a silicon film as a precursor film by LP-CVD andthen anneals it. Regarding the relation between conditions of depositionby LP-CVD and subsequent heating and the crystal grain size, it is knowndesirable to form amorphous silicon at a temperature not higher than580° C. and anneal it at about 600° C., for example, in order to obtainpolycrystalline silicon with a large grain size. In case of solid phasegrowth by heating, if an amorphous silicon film is annealed at 600° C.for 12 hours, for example, the crystal grain size reaches 100 through2000 nm. In general, the larger the grain size, the higher the mobility.However, in solid phase growth by annealing, crystal patterns are notconstant, and a lot of twin crystal defects and dislocation defects areobserved in crystal grains through a crystal image. Because of thesedefects, although polycrystalline. silicon obtained by solid phasegrowth has a large grain size, its mobility is only around 70 cm²/V·s.

Laser annealing has also been used as a technique for makinghigh-quality polycrystalline silicon. With this method, silicon thinfilms can be crystallized at relatively low temperatures without heatingthe entire substrate so high. When laser light is irradiated onto asilicon thin film to be crystallized, the energy is absorbed only by thevery surface of the silicon thin film. Thereafter, the inner portion ofthe thin film melts due to heat conduction, and re-crystallizes duringits cooling process. In polycrystalline silicon films made in thismanner, crystal grains are distributed about uniformly. Also whenreviewing its lattice image, crystal defects are less than those bysolid phase growth. However, in the case of laser annealing, the crystalgrain size is relatively as small as 200 through 300 nm, a lot ofcrystal grain boundaries exist, and the mobility is around 40 cm²/V·s.

There is a recently developed technique for reducing crystal defects byadding laser annealing by excimer laser light after solid phase growthby annealing. It is disclosed, for example, in Japanese Patent Laid-OpenPublication No. sho 62-104021 and Japanese Patent Laid-Open PublicationNo. hei 7-302913. However, even with this method, mobility of thin filmtransistors has not been increased sufficiently. The second object ofthe-invention is to obtain a higher mobility by optimizing conditions oflaser annealing after solid phase growth. Additionally, in thetechnology combining solid phase growth and laser annealing, the crystalgrain size of the polycrystalline silicon thin film is basicallydetermined by solid phase growth. In order to obtain thin filmtransistors with a higher mobility, the grain size of the poly crystalmust be increased more. This is also the second object of the invention.Furthermore, it is the second object of the invention to provide asilicon thin film having a still higher quality by employing adeposition method as a replacement for solid phase growth in combinationwith laser annealing.

Here is explained still another problem of conventional techniques.Heretofore, solid phase growth or annealing has been used as a methodfor making a polycrystalline semiconductor thin film to be used as theactive layer of thin film transistors. In solid phase growth, althoughcrystal grains contained in the polycrystalline semiconductor thin filmgrow to a size as large as about 1 μm, it contains a lot of crystaldefects such as dislocation. Therefore, mobility of the thin filmtransistors is 100 cm²/V·s or less in terms of the N channel. Incontrast, in the case of crystallization by laser annealing, althoughcrystal grains contain less crystal defects, since the crystal grainsize can increase only to 200 through 300 nm, approximately, mobility ofthe thin film transistors also remain in the level equivalent to orlower than that by solid phase growth. There is a recently proposedmethod for repairing crystal defects by conducting laser annealing aftersolid phase growth, and this method can improve the mobility toapproximately 130 cm²/V·s. However, this method uses laser annealingonly for repairing crystal defects, and since the crystal grain size ofthe polycrystalline semiconductor thin film is determined by solid phasegrowth in the preceding step, further increase of the crystal grain sizecannot be expected. In order to obtain thin film transistors whosemobility exceeds 300 cm²/V·s, more increase of the crystal grain size isindispensable, and attainment of this requirement is the third object ofthe invention.

DISCLOSURE OF INVENTION

To accomplish the first object of the invention, a method formanufacturing a thin film semiconductor device according to theinvention basically includes a deposition step for making anon-single-crystalline semiconductor thin film on a surface of aninsulating substrate, an annealing step for irradiating laser light toonce heat and melt the non-single-crystalline semiconductor thin filmand then changing it into a poly crystal in its cooling process, and aprocessing step for integrally forming thin film transistors using thesemiconductor thin film of the polycrystal as the active layer. As aparticular feature, in the annealing step, laser light having the pulsewidth of 50 ns or more is irradiated onto the semiconductor thin film byusing an excimer laser source. In the annealing step, preferably afterthe laser light is shaped to have a rectangular cross section whose eachside is not shorter than a predetermined length (for example 10 mm), thesurface of the semiconductor thin film is irradiated sequentially bymoving the laser light step by step so that the sides of the rectangularcross section partly overlap. In this case, frequency of irradiation ofthe laser light per each stepping movement is selected so that thefrequency of overlapping irradiation of the laser light onto the samepart of the surface of the semiconductor thin film is a predeterminednumber.

According to the invention, for making thin transistors using thepolycrystalline semiconductor of polycrystalline silicon, for example,as the active layer on the insulating substrate in a low-temperatureprocess, amorphous silicon is first made on the insulating substrate bylow-pressure chemical vapor deposition (LP-CVD), plasma CVD orsputtering. After that, by using an excimer laser light source, thelaser light is irradiated onto the semiconductor thin film to change theamorphous silicon into polycrystalline silicon. In some cases,polycrystalline silicon having a relatively small grain size may bechanged into polycrystalline silicon having a relatively large grainsize by irradiation of the laser light. To generalize them altogether,amorphous silicon and polycrystalline silicon having a small grain sizeare called non-single-crystalline silicon, and in this embodiment,non-single-crystalline silicon is changed into polycrystalline siliconby irradiation of the laser light. Unlike the conventional techniques,in the present invention, laser light released from an excimer lasersource having the pulse width of 50 ns or more is shaped into arectangle by an appropriate optical system, and it is irradiated ontothe semiconductor thin film step by step. For example, the laser lightis shaped by an optical system to have a rectangular cross section of 10mm×10 mm or larger in terms of the irradiated area of the semiconductorthin film. In this embodiment, laser light is irradiated while moving itstep by step to partly overlap it so that the same position isirradiated by the laser light at least two times at least in a part ofthe entire area of the insulating substrate. By employing this mode ofirradiation, it is possible to make a polycrystalline semiconductor thinfilm having a uniform, large grain size sufficiently acceptable as theactive layer of high-mobility, high-performance thin film transistors.More specifically, polycrystalline silicon having the grain sizeexceeding 300 to 1000 nm can be made uniformly throughout the entiresurface of the substrate.

To attain the second object of the invention, the following means isemployed. That is, the invention relates to a method for manufacturing asemiconductor transistor, which forms on an insulating substrate amulti-layered structure basically including a semiconductor thin film,gate insulating film stacked on one surface of the semiconductor thinfilm and gate electrode stacked on the semiconductor thin film via thegate insulating film. According to one aspect of the invention, the thinfilm transistor is manufactured in the following process. Firstconducted is a forming step to form on the insulating substrate thesemiconductor thin film containing polycrystalline grains. Morespecifically, a deposition step is conducted to stack on the insulatingsubstrate an amorphous semiconductor thin film or a polycrystallinesemiconductor thin film made up of crystal grains of a relatively smallgrain size. Next conducted is a solid phase growth step to grow crystalgrains with a relatively small grain size in solid phase by annealingthe semiconductor thin film. Alternatively, a semiconductor thin filmcontaining polycrystalline grains may be stacked directly on theinsulating substrate by chemical vapor deposition using a catalyst.After that, a laser annealing step is conducted to remove residualdefects in the crystal grains by using laser light in the form of pulseshaving the emission time of 100 ns or more and irradiating thesemiconductor thin film with an energy not inviting destruction ofcrystal grains of large sizes. Preferably, in the laser annealing step,laser light is irradiated onto the semiconductor thin film with theenergy of 500 to 600 J/cm².

According to another aspect of the invention, the thin film transistoris manufactured in the following process. First conducted is adeposition step to stack on the insulating substrate an amorphoussemiconductor thin film or a polycrystalline semiconductor thin filmmade up of crystal grains with a relatively small grain size. Therefollows the solid phase growth step in which the semiconductor thin filmis annealed to grow crystal grains with a larger grain size in solidphase. Next comes the laser annealing step in which by using laser lightin the form of pulses, energy as moderate as not causing destruction oflarge size crystal grains is irradiated onto the semiconductor thin filmto remove residual defects in the crystal grains. After that, anadditional solid phase growth step is conducted to anneal thesemiconductor thin film again and grow crystal grains with a stilllarger grain size in solid phase. Preferably, after the additional solidphase growth step, moderate energy not inviting destruction oflarge-size crystal grains is irradiated again onto the semiconductorthin film by using laser light in the form of pulses, and an additionallaser annealing step is conducted to remove defects produced in theadditional solid phase growth step.

This aspect of the invention involves a method for making asemiconductor thin film. That is, the method for making a semiconductorthin film according to the invention comprises a forming method forforming a semiconductor thin film on an insulating substrate at atemperature not higher than 400° C. by chemical vapor deposition using acatalyst, and a laser annealing step for improving the quality of thesemiconductor thin film by irradiating laser light in the form of pulseshaving emission time not shorter than 100 nm on the insulatingsubstrate. More specifically, in the forming step, a polycrystallinesemiconductor thin film containing crystal grains is formed by chemicalvapor deposition using a catalyst, and in the laser annealing step,laser light with an energy not inviting destruction of the crystalgrains is irradiated to remove defects existing in the crystal grainsand thereby improve the quality of the semiconductor thin film.Preferably, the forming step forms a semiconductor thin film containinghydrogen by 1% or less and having a thickness not thicker than 50 nm isformed on the insulating substrate by chemical vapor deposition using acatalyst. Preferably, this forming step forms the semiconductor thinfilm in a reaction chamber which can be evacuated, and the laserannealing step irradiates laser light on the insulating substratewithout breaking the evacuated condition of the reaction chamber. If sodesired, the forming step and the laser annealing step are repeatedalternately until the semiconductor thin film grows to a predeterminedthickness.

According to one aspect of the invention, the polycrystallinesemiconductor thin film having large-size crystal grains is obtained bysolid phase growth using annealing or chemical vapor deposition using acatalyst. After that, laser annealing is conducted to remove residualdefects in the crystal grains. By increasing the grain size by solidphase growth, etc. and removal of defects by laser annealing, mobilityof the thin film transistors can be increased. In this case, when laserannealing is conducted by using the pulse-mode laser light havingemission time (relaxation time) not shorter than 100 ns, crystal defectscan be removed efficiently. Therefore, removal of defects can beimproved significantly by using laser pulses having a longer emissiontime than conventional ones. To maintain the crystal grain size obtainedin the solid phase growth, it is important that the energy applied tothe semiconductor thin film in the laser annealing step be controlled ina level not inviting destruction of the large-size crystal grains (forexample, 500 through 600 cm²/V·s). In the laser annealing, by removingresidual crystal defects without producing new crystal defects, a highmobility can be attained. In the other aspect of the invention, afterthe laser annealing step, crystal grains with a still larger grain sizeare grown in solid phase by annealing the semiconductor thin film again.As a result, a further improvement of the mobility can be attained. Byconducting laser annealing after the first solid phase growth, crystaldefects decrease, and a stress in the thin film is alleviated. Byconducting the second solid phase growth in this status, the crystalgrain size is increased efficiently. In the other aspect of theinvention, the semiconductor thin film suitable as the active layer ofthin film transistors is made by combining chemical vapor depositionusing a catalyst (catalytic CVD) and laser annealing. Catalyst CVD iscapable of forming the polycrystalline semiconductor thin film ofpolycrystalline silicon, for example, at a low temperature not higherthan 400° C. By processing this semiconductor thin film by laserannealing, defects contained in the crystal grains can be removed. Sincecatalytic CVD and laser annealing are low-temperature processes, it ispossible to make thin film transistors in a low-temperature processwhile maintaining the property of the thin film transistors.

Furthermore, to attain the third object of the invention, the followingmeans is employed. That is, there is provided a method for manufacturinga thin film transistor, which forms on an insulating substrate amulti-layered structure including a semiconductor thin film, a gateinsulating film stacked on one surface of the semiconductor thin film,and a gate electrode stacked on the semiconductor thin film via the gateinsulating film, and the method comprises a forming step for forming onthe insulating substrate a semiconductor thin film containingpolycrystalline grains, and a laser annealing step for irradiating laserlight in the mode of pulses having emission time not shorter than 50 nsand thereby removing residual defects in the crystal grains to increasethe size of the crystal grains. Preferably, in the laser annealing step,irradiation of the pulse-mode laser light is repeated a number of timesnecessary for the crystal grains to grow to a predetermined size. In thelaser annealing step, the pulse-mode laser light is repeatedlyirradiated in a cycle not shorter than ⅕ Hz. Still in the laserannealing step, the laser light is irradiated onto the semiconductorthin film under the energy density of 400 through 600 cm²/V·s. Further,the laser annealing step uses pulse-mode laser light having emissiontime not shorter than 100 ns. Furthermore, the laser annealing stepirradiates laser light having an irradiation area not smaller than 5 cm²onto the semiconductor thin film. The forming step includes a depositionstep for stacking an amorphous semiconductor thin film or apolycrystalline thin film made of crystal grains with a relatively smallgrain size on an insulating substrate, and a solid phase growth step forannealing the semiconductor thin film to grow crystal grains with alarger grain size in solid phase. Alternatively, the forming step stacksa semiconductor thin film containing polycrystalline grains on theinsulating substrate by chemical vapor deposition using a catalyst.

According to the invention, in the manufacturing process of a thin filmtransistor, the semiconductor thin film containing polycrystallinegrains is formed on the insulating substrate by solid phase growth orcatalytic chemical vapor deposition. After that, by repeatedlyirradiating pulse-mode laser light, residual defects in the crystalgrains are remedied, and the crystal grains are enlarged. As a result, ahigh-mobility semiconductor thin film can be obtained. Especially whenthe number of times of irradiation of pulse-mode laser light isdetermined adequately, a polycrystalline semiconductor thin filmcontaining crystal grains with a predetermined size can be made.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram showing a conventional laser annealingmethod. FIG. 2 is a schematic diagram showing a major part of amanufacturing process of a thin film semiconductor device according tothe invention. FIG. 3 contains graphs schematically showing the pulsewidth of laser light used in the manufacturing method of the thin filmsemiconductor device according to the invention. FIG. 4 contains planviews schematically showing an annealing step included in themanufacturing method of the thin film semiconductor device according tothe invention. FIG. 5 contains plan views also schematically showing theannealing step. FIG. 6 contains process diagrams showing an embodimentof the manufacturing method of the thin film semiconductor deviceaccording to the invention. FIG. 7 is a schematic perspective viewshowing an active matrix display device using the thin filmsemiconductor device made by the method shown in FIG. 6. FIG. 8 containsprocess diagrams showing a major part of a manufacturing process of athin film transistor according to the invention. FIG. 9 is a graphshowing relation between laser light irradiation energy and mobility ofthe thin film transistors. FIG. 10 is a schematic diagram illustrating acatalytic CVD apparatus used in the manufacturing process of the thinfilm transistor according to the invention. FIG. 11 contains processdiagrams showing an embodiment of the manufacturing method of the thinfilm transistor according to the invention. FIG. 12 contains processdiagrams illustrating the embodiment of the manufacturing method of thethin film transistor according to the invention. FIG. 13 containsprocess diagrams illustrating the embodiment of the manufacturing methodof the thin film transistor according to the invention. FIG. 14 containsschematic diagrams showing a method for forming a silicon film accordingto the invention. FIG. 15 additionally contains process diagrams showinganother embodiment of the manufacturing method of the thin filmtransistor according to the invention. FIG. 16 is a graph showingrelation between the number of times of laser light irradiation and thegrain size of a polycrystalline semiconductor thin film. FIG. 17 is agraph showing relation between the number of times of laser lightirradiation and the mobility of the thin film transistor. FIG. 18 is agraph showing relation between irradiation energy density of laser lightand mobility of thin film transistors.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the invention are explained below in detail withreference to the drawings. FIG. 2 schematically illustrates a major partof a manufacturing process of a thin film semiconductor device, which isrelated to the first object of the invention. The present inventionbasically executes a deposition step for stacking anon-single-crystalline semiconductor thin film 2 on one surface of aninsulating substrate 1, an annealing step for irradiating laser light 50to once heating and melting the non-single crystalline semiconductorthin film 2 and thereafter changing it into a polycrystal in its coolingprocess, and a processing step for integrally forming a thin filmtransistor having the polycrystallized semiconductor thin film as itsactive layer.

FIG. 2 schematically illustrates the annealing step, among others. Thelaser annealing apparatus used in this annealing step has a laseroscillator 51, attenuator 52, optical system 53 including a homogenizer,chamber 54 and stage 55. The laser oscillator 51 includes an excimerlaser source and intermittently emits laser light 50 having a pulsewidth not shorter than 50 ns. The optical system 53 including thehomogenizer receives the laser light emitted from the laser oscillator51 via the attenuator 52, then shapes it to have a rectangular crosssection with each side being 10 mm or more, and irradiates it onto thesemiconductor thin film 2. The insulating substrate 1 having formed thenon-single-crystalline semiconductor thin film 2 is set on the stage 55inside the chamber 54. The stage 55 is movable in XY directions. In thisembodiment, the laser light 50 is moved step by step relative to thesemiconductor thin film 2 so that the sides of the rectangular crosssection partly overlap, and are sequentially irradiated onto thesurface. Preferably, the number of times of laser light irradiation pereach stepping movement is previously set so that any particular part ofthe surface of the semiconductor thin film 2 is irradiated by apredetermined number of shots of laser light 50. The attenuator 52 isused to adjust the energy of the laser light emitted from the laseroscillator 51. The optical system 53 shapes the laser light to have arectangular cross section and also adjusts it so that the energy bedistributed uniformly over the entire rectangular cross section. Thelaser anneal apparatus used in the invention has a relatively largeoutput power and can output laser pulses having an emission time notshorter than 50 ns. In contrast, conventional laser anneal apparatusesoutput laser pulses with an emission time of 20 through 50 ns, and theirpowers are insufficient for removal of crystal defects.

FIG. 3 schematically shows pulse widths of laser light. In thisdescription, the width of the 10% level relative to the peak level ofthe laser light is defined as the pulse width. As shown in FIG. 3A, thepulse width of an excimer laser source used in conventionalcrystallization annealing is less than 50 ns. In contrast, the pulsewidth of the laser light emitted from the excimer laser source used inthe embodiment exceeds 50 ns as shown in FIG. 3B, and it is typicallyaround 200 ns. FIG. 3A and FIG. 3B show different pulse waveforms forthe purpose of demonstrating that regardless of the pulse waveforms, thewidth of the 10% level relative to the peak level is measured.Essentially, therefore, no correlation exists between the pulse waveformand the pulse width. Therefore, a pulse waveform as shown in FIG. 3A isalso acceptable if it has a pulse width beyond 50 ns.

Table 1 given below shows the performance of the laser anneal apparatusused in the annealing step.

TABLE 1 Laser Anneal Maximum Grain Apparatus Pulse Width (ns) Size (nm)A 25 350 B 45 350 C 220 1500

The laser anneal apparatus A is a conventional apparatus having thepulse width of 25 ns, configured to shape laser light into a line beamwith the width of 0.5 mm and irradiate it onto the semiconductor thinfilm while scanning the line beam in its width direction. Scanning bythe line beam is conducted to make irradiated regions partly overlap sothat any particular portion is irradiated 50 times. The maximum grainsize of polycrystalline silicon obtained thereby was 350 nm. The laseranneal apparatus B is also a conventional apparatus having the pulsewidth of 45 ns. Here again, laser light was shaped into a line beamhaving the width of 0.5 mm, and irradiated onto the semiconductor thinfilm in the overlapping manner. The maximum grain size of thepolycrystalline silicon semiconductor thin film obtained thereby is 350nm. In contrast, the laser anneal apparatus C is that used in thepresent invention, and its pulse width is 220 ns. Laser light having thepulse width of 220 ns was shaped to make a 10 mm×10 mm rectangular crosssection, and it was irradiated while being scanned in the XY directionsso that the sides of the rectangle overlap. In each stepping movement,the laser light was irradiated in pulses repeating 10 times. The maximumgrain size of the polycrystalline silicon semiconductor thin filmobtained thereby reaches 1500 nm.

Table 2 demonstrates relations between the number of irradiation shotsand the grain size in the laser anneal apparatus C. That is, it shows aresult of experimental investigation of numbers of irradiation shots oflaser light repeatedly irradiated under a constant energy onto aparticular portion by using the laser anneal apparatus C and grain sizesobtained thereby. The grain size of polycrystalline silicon increaseswith the increase in number of irradiation shots, and becomessubstantially constant after the number of irradiation shots reaches 10shots. Even when the number of irradiation shots is increased to morethan 10 shots, the crystal grain size does not change so much. That is,it comes in saturation.

TABLE 2 Number of Shots Grain Size (nm) 1 140 2 180 4 350 5 470 10 150020 1400

FIG. 4 schematically illustrates an embodiment in which by using thelaser anneal apparatus C shown in Table 1 and Table 2, amorphous siliconstacked on a glass substrate was changed uniformly into polycrystallinesilicon. In the case where a semiconductor thin film formed on aninsulating substrate 1 larger than the cross-sectional area of the laserlight is irradiated, it is necessary to scan the laser light relative tothe insulating substrate 1. As shown in FIG. 4A, this example irradiatesthe laser light shaped into a rectangle with each side beyond 10 mm inits cross section being irradiated four times on each portion. After acertain portion of the insulating substrate 1 is irradiated by the laserlight four times, they are relatively moved to a position where the nextirradiated region slightly overlaps the former irradiated region alongtheir sides, and the next region is also irradiated four times. As aresult, the overlapping portion of consecutive rectangularcross-sectional areas becomes the region irradiated 8 times. Energy ofthe laser light irradiated onto a certain portion may be constant in allof four shots, or may be changed appropriately among these four shotsdepending under certain conditions. Although explanation has been madeon the example in which the stage supporting the insulating substrate 1does not move during four shots of irradiation, the stage may be movedafter each shot of irradiation or may be moved continuously throughoutthe irradiation. This manner of irradiation results in making regionsirradiated 8 times as shown in FIG. 4B and regions irradiated 16 timesas shown in FIG. 4C due to the overlapping between consecutive shots. Inthis case, as apparent from reference to Table 2, polycrystallinesilicon of grain sizes from 35 nm to 1500 nm can be obtained throughoutthe area of the insulating substrate 1.

Demands for uniformity all over the area of thin film transistors usedin an active matrix display device are different depending upon thespecification of the display device and built-in circuit arrangementsthereof. In order to fabricate a high-performance active matrix displaydevice having the need for polycrystalline silicon with more uniform andlarger grain sizes, it is sufficient to irradiate the laser light 10times on each portion. In this manner, polycrystalline silicon with veryuniform grain sizes around 1500 nm can be made throughout the entiresurface of the glass substrate.

In a display device not required to be so high in quality, theirradiation method shown in FIG. 5 may be employed. In this case, thereare produced, in the area of the glass substrate, portions irradiatedonly once as shown in FIG. 5A, portions irradiated twice as shown inFIG. 5B and portions irradiated four times as shown in FIG. 5C, andvariety in grain size of the polycrystalline silicon is 140 through 350nm with reference to Table 2. As explained above, depending on thespecification of the display device and built in circuit arrangementsthereof, thin film transistors sufficiently acceptable for use in activematrix display devices even with this level of variety in grain size canbe made.

FIG. 6 contains process diagrams showing an embodiment of themanufacturing method of a thin film semiconductor device according tothe invention. Here is taken a method for manufacturing a thin filmtransistor having a bottom-gate structure. First as shown in FIG. 6A,Al, Ta, Mo, W, Cr, Cu or an alloy of any of them is deposited to athickness of 100 through 200 nm on an insulating substrate made ofglass, for example, and it is patterned into a gate electrode 5.

Next as shown in FIG. 6B, a gate insulating film is formed on the gateelectrode 5. In this example, a two-layered structure of gate nitridefilm 3 (SiN_(x))/gate oxide film 4 (SiO₂) was used as the gateinsulating film. The gate nitride film 3 was stacked by plasma enhancedCVD (PE-CVD) using a mixture of SiH₄ gas and NH₃ gas as the sourcematerial gas. Normal pressure CVD or Reduced pressure CVD may be alsoused instead of PE-CVD. In this embodiment, the gate nitride film wasstacked to the thickness of 50 nm. Subsequently to the stacking of thegate nitride film 3, the gate oxide film 4 is stacked up to a thicknessaround 200 nm. Furthermore, a semiconductor thin film 2 made ofamorphous silicon was continuously stacked on the gate oxide film 4 upto a thickness around 30 through 80 nm. The two-layered gate insulatingfilm and amorphous semiconductor thin film 2 were stacked consecutivelywithout breaking the vacuum system of the deposition chamber. Whenplasma CVD is used for the above deposition, annealing is conducted in anitrogen atmosphere at 400 through 450° C. for about one hour to removehydrogen contained in the amorphous semiconductor thin film 2. So-calleddehydrogenation annealing is conducted. After that, laser light 50 isirradiated to crystallize the amorphous semiconductor thin film 2.Usable as the laser light 50 is an excimer laser beam. So-called laserannealing is a powerful means for crystallizing semiconductor thin filmsat process temperatures not higher than 600° C. In this embodiment,laser light 50, which is excited in mode of pulses and shaped into arectangular geometry, is irradiated onto the amorphous semiconductorthin film 2 to crystallize it. Pulse width of the laser light 50 isbeyond 50 ns, and the size of its rectangular cross section exceeds 100mm×10 mm. For example, the pulse width is chosen to 220 ns, and therectangular cross section is chosen to 30 mm×70 mm.

As shown in FIG. 6C, SiO₂ is stacked on the polycrystallinesemiconductor thin film 2 already crystallized in the preceding step upto a thickness around 100 through 300 nm by plasma CVD, for example.This SiO₂ is patterned into a predetermined configuration to form anetching stopper film 16. In this case, the etching stopper film 16 ispatterned to align with the gate electrode 5 by using a back exposuretechnique. The portion of the polycrystalline semiconductor thin film 2located right under the etching stopper film 16 is protected as achannel region Ch. After that, using the etching stopper film 16 as amask, an impurity (for example, P⁺ ions) is injected into thesemiconductor thin film 2 by ion doping to form an LDD region. Doseamount used here is, for example, 6×10¹² through 5×10¹³/cm². Further,after a photo resist is coated and patterned to cover the stopper film16 and LDD regions at opposite sides thereof, an impurity (for example,P⁺ ions) is injected in a high concentration by using the photo resistas a mask to form the source region S and the drain region D. Forinjection of the impurity, ion doping may be used, for example. This isa method for injecting the impurity under electric field accelerationwithout conducting mass separation. In this example, the source region Sand the drain region D were made by injecting the impurity by the doseamount around 1×10¹⁵/cm². Although not shown, if a p-channel thin filmtransistor is to be made, ion doping may be conducted with the doseamount around 1×10¹⁵/cm² by changing the impurity from P⁺ ions to B⁺ions after covering the region of the n-channel thin film transistorwith a photo resist.

Subsequently, the impurity injected into the polycrystallinesemiconductor thin film 2 is activated. Here again, laser activationannealing using an excimer laser source is conducted. That is, they areirradiated onto the glass substrate 1 and activate the impurity injectedinto the polycrystalline semiconductor thin film 2.

Finally, as shown in FIG. 6D, approximately 200 nm thick SiO² is stackedas an inter-layer insulating film 6. After the stacking of theinter-layer insulating film 6, SiN_(x) is stacked to a thickness ofabout 200 through 400 nm by plasma CVD as a passivation film (cap film)8. In this stage, annealing is conducted in a nitrogen gas atmosphere,forming gas atmosphere or vacuum at about 350° C. for one hour todisperse hydrogen atoms contained in the inter-layer insulating film 6into the semiconductor thin film 2. Thereafter, a contact hole isopened, Mo, Al, or the like, is deposited to a thickness of 200 through200 nm by sputtering, and it is patterned into a predeterminedconfiguration to form a wiring electrode 7. Further, a smoothing layer10 of acrylic resin, for example, is coated up to around 1 μm, and acontact hole is opened. After a transparent conductive film of ITO orIXO is made on the smoothing layer 10 by sputtering, it is patternedinto a predetermined configuration to form a pixel electrode 11.

Next explained is an example of active matrix display device using thethin film transistor made by the invention with reference to FIG. 7. Asillustrated, the display device has a panel structure including a pairof insulating substrates 101, 102 and an electrooptic substance 103 heldbetween them. Used as the electrooptic substance 103 is a liquid crystalmaterial, for example. The lower insulating substrate has a pixel arrayportion 104 and a drive circuit portion integrated thereon. The drivecircuit portion is divided into a vertical scanner 105 and a horizontalscanner 106. Further formed at the tope end of the peripheral portion ofthe insulating substrate 101 is a terminal portion 107 for externalconnection. The terminal portion 106 connects to the vertical scanner105 and the horizontal scanner 106 via a wiring 108. Formed in the pixelarray portion 104 are gate wirings 109 in line directions and signalwirings 110 in column directions. At the crossing of both these wirings,pixel electrodes 111 and thin film transistors 112 for driving them areformed. The gate electrode of each thin film transistor 112 is connectedto the gate wiring 109, its drain region to corresponding one of thepixel electrodes 111, and its source region to corresponding one of thesignal wirings 110. The gate wirings 109 connect to the vertical scanner105 whereas the signal wirings 110 connect to the horizontal scanner106. The thin film transistors 112 for switching and driving the pixelelectrodes 111 and thin film transistors contained in the verticalscanner 105 and the horizontal scanner 106 are made according to theinvention. Further, in addition to the vertical scanner and thehorizontal scanner, a video driver and a timing generator can be alsointegrated in the insulating substrate 101.

FIG. 8 contains process diagrams showing a major part of themanufacturing method of a thin film transistor dealing with the secondobject of the invention. The thin film transistor has a multi-layeredstructure including a semiconductor thin film, gate insulating filmstacked on one surface thereof, and gate electrode stacked on thesemiconductor thin film via the gate insulating film, and it is formedon an insulating substrate. The thin film transistor is manufactured inthe process shown below. First in the step shown in FIG. 8A, anamorphous semiconductor thin film or a polycrystalline semiconductorthin film 2 made of crystal grains having a relatively small grain sizeis stacked on the insulating substrate 1. For example, a semiconductorthin film 2 made of polycrystalline silicon is stacked to a thickness of40 through 75 nm by LP-CVD. After that, Si⁺ accelerated by an electricfield is injected into the semiconductor thin film 2 to change it intoan amorphous phase. Thereafter, the semiconductor thin film 2 isannealed to produce crystal grains with a relatively large grain size bysolid phase growth. For example, by annealing it at 600° C. for 12hours, crystal grains grow to grain sizes of about 1000 through 2000 nm.Then the process moves to the step shown in FIG. 8B in which, by usingpulse-mode laser light having an emission time not shorter than 100 ns,an energy not inviting destruction of large size crystal grains isirradiated onto the semiconductor thin film 2 to remove residual defectsin the crystal gains. More specifically, by using an excimer lasersource having an emission time (relaxation time) of 200 ns andirradiating an energy in the level of 500 through 600 mJ/cm², crystaldefects are removed. In this case, it is important to conduct excimerlaser annealing (ELA) under the conditions in which the crystal obtainedby solid phase growth does not melt completely. After that, the processmoves to the step shown in FIG. 8C in which the semiconductor thin film2 is patterned to meet the device region. The semiconductor thin film 2patterned into the form of an island is covered by a gate insulatingfilm 3. Then the process moves to the step shown in FIG. 8D and makesthe gate electrode 5 on the gate insulating film 3. By injecting animpurity into the semiconductor thin film 2 in self alignment by usingthe gate electrode 5 as a mask, the thin film transistor having atop-gate structure is obtained. Needless to say, the invention isapplicable not only to thin film transistors having a top-gate structurebut also to thin film transistors having a bottom-gate structure.

Depending on circumstances, an additional solid phase growth step may beinserted between the step shown in FIG. 8B and the step shown in FIG.8C. That is, it is also possible to anneal the semiconductor thin film 2once again to grow still larger crystal grains by solid phase growth. Byconducting the additional solid phase growth under the condition wheredislocation or other crystal defects are decreased by ELA and the stressin the thin film is alleviated, the grain size can be increased furthermore. Preferably, after the additional solid phase growth step, by usingpulse-mode laser light and irradiating an energy in the level notinviting destruction of large size crystal grains, defects produced inthe additional solid phase growth step are removed. In the solid phasegrowth process, a lot of dislocation occurs in the crystal. It willbecome one of factors of a decrease of the mobility of the thin filmtransistor. By heating the semiconductor thin film for a short time (forexample, 200 ns) by using excimer laser light, this dislocation can beremoved. If the solid phase growth is conducted at the temperature of600° C. for 12 hours, crystal grains grow beyond 1000 nm. After that,when laser annealing is conducted according to the invention, mobilityof the thin film transistor increases. In contrast, if the mobility inthe level of the conventional one is acceptable, conditions of the solidphase growth may be alleviated to shorten the time or lower the heatingtemperature. Energy of the laser annealing is preferably adjustedaccordingly.

FIG. 9 contains the measured data demonstrating the relation between theirradiation energy and mobility of the thin film transistor in the laserannealing step. As apparent from the graph, if laser annealing isconducted with an irradiation energy in the level of 500 through 600mJ/cm², since crystal grains obtained by the solid phase growth aremaintained as they were, mobility around 130 cm²/V·s is obtained. Whenthe irradiation energy exceeds 600 mJ/cm², since the crystal is moltenby laser annealing, large grain sizes obtained by the solid phase growthcannot be maintained, and the mobility decreases below 10 cm²/V·s. Whenthe irradiation energy decreases below 400 mJ/cm², removal of crystaldefects is insufficient, and the mobility does not become high.

In the embodiment explained above, the semiconductor thin film iscrystallized by solid phase growth. Instead, a polycrystallinesemiconductor thin film can be stacked directly on the insulatingsubstrate by so-called catalytic CVD. If the polycrystallinesemiconductor thin film stacked by catalytic CVD is annealed, defectscontained in the crystal grains can be removed. Catalytic CVD is amethod which creates a semiconductor thin film of polycrystallinesilicon while maintaining the temperature of the substrate itself at alow temperature without using plasma or optical excitation process, byblowing a source material gas onto a heated catalytic body located nearan insulating substrate, thereby decomposing all or part of the sourcematerial gas by using catalytic cracking reaction between thecatalyst-and the source material gas, and then transporting thedecomposed and stacked seed to the insulating substrate. FIG. 10 is anexplanatory diagram of a creation method of a polycrystalline siliconsemiconductor thin film-by catalytic CVD. In FIG. 10, 71 refers to areaction chamber. 73 is a catalytic body which may be a heater liketungsten, for example. 74 denotes a source material gas supply tube forsupplying a source material gas. The source material gas is a mixed gasof a silane compound of a silane group element such as silane anddisilane. 75 denotes a heater for heating the insulating substrate 1. 76is a power supply source for supplying power to the catalytic body 73.In this structure, the insulating substrate 1 is heated at a lowtemperature around 500° C. by the heater 75. The source material gas issupplied to the source material gas supply tube 74. The source materialgas contacts the catalytic body 73, and all or part of the siliconcompound in the source material gas is decomposed by this contact togenerate silicon (Si) seeds. Decomposed Si seeds, silicon compound whichwas not decomposed, and gas of other substances (hydrogen gas or thelike) move onto the insulating substrate 1. Then, Si seeds stack on thesurface of the insulating substrate 1 and form the semiconductor thinfilm 2 which is made up of polycrystalline silicon. Catalytic CVD isdisclosed in Japanese Patent Laid-Open Publication No. hei 8-250438, forexample.

Next referring to FIG. 11 through FIG. 13, explanation is made below ofan embodiment of the thin film transistor manufacturing method accordingto the invention. This embodiment forms a thin film transistor of atop-gate structure in a high-temperature process in which the processtemperature reaches 850° C. or higher. The invention, however, is notlimited to it, and it is also applicable when making thin filmtransistors of a bottom-gate structure. First in the step shown in FIG.11A, the semiconductor thin film 2 is formed on an insulating substrate1 made of quartz. There was stacked polycrystalline silicon with arelatively small grain size to the thickness of 75 nm at a depositiontemperature in the range of 600° C. through 700° C. by LP-CVD. Theprocess moves to the step shown in FIG. 11B, and implants Si ions intothe semiconductor thin film 2 by ion implantation to once change thepolycrystalline silicon to amorphous phase. In this case, ionimplantation was conducted twice by setting the acceleration energy ofSi ions at 40 keV and 60 keV, respectively. The process goes to the stepshown in FIG. 11C, and changes the semiconductor thin film 2 fromamorphous silicon to polycrystalline silicon with a relatively largegrain size by solid phase growth (SPG). Process conditions employed hereare 600° C. and 12 hours for heating. The process then moved to the stepshown in FIG. 11D in which by first ELA, defects contained in thecrystal grains of the semiconductor thin film 2 were removed. Asconditions used here, by using excimer laser light with the emissiontime (relaxation time) of 200 ns, an energy in the level of 500 to 600mJ/cm² was irradiated. Then the process moved to the step shown in FIG.11E, and enlarged the crystal grains contained in the semiconductor thinfilm 2 still further by conducting second SPG. The process next moved tothe step shown in FIG. 11F, and crystal defects produced by second SPGwere removed by second ELA. The process thereafter goes to the stepshown in FIG. 11G, and the semiconductor thin film 2 is patterned tomeet the geometry of individual thin film transistor regions. In thispatterning step, photolithography and etching are used. Further, thegate insulating film 3 is formed on the surface of the semiconductorthin film 2. More specifically, the semiconductor thin film 2 is heatedin an oxygen gas atmosphere at 1000° C. for 60 minutes. As a result, thesurface of the semiconductor thin film 2 is thermally oxidized, and thegate insulating film 3 of silicon oxide is formed up to the thicknessaround 60 nm. As a result, thickness of the semiconductor thin film 2 isreduced to 45 nm.

The process moves to the step shown in FIG. 12H, and a gate insulatingfilm 4 is stacked on the gate insulating film 3. In this step, HTO (hightemperature oxide) is stacked to 30 nm at the process temperature of800° C. by CVD. It is additionally heated at 1000° C. for 10 minutes toclosely pack the gate insulating film 4 of HTO. The process moves to thestep shown in FIG. 12I, and the gate electrode 5 is formed on the gateinsulating film 4. More specifically, after polycrystalline silicon isstacked to a thickness in the range of 350 through 450 nm, it ispatterned into a predetermined configuration to form the gate electrode5. Impurity phosphorus is diffused into the gate electrode 5 at theprocess temperature of 1000° C. to reduce its resistance. The processmoves to the step shown in FIG. 12J in which by using the gate electrode5 as a mask, impurity As is injected into the semiconductor thin film 2by ion implantation, using the dose amount of 3×10¹⁵/cm², for example.As a result, the source region S and the drain region D of the n-channelthin film transistor are formed. Immediately under the gate electrode 5,a channel region CH is maintained between the source region and thedrain region D. If p-channel thin film transistors are to be made,impurity B may be injected into the semiconductor thin film 2 by ionimplantation, using the dose amount of 1×10¹⁵/cm², for example. Theprocess moves to the step shown in FIG. 12K, and the gate electrode 5 iscovered with a first inter-layer insulating film 6. In this example, PSGcontaining phosphorus by 4% was stacked to 600 nm at 400° C. by LP-CVD.After that, the semiconductor thin film 2 was heated by annealing orlaser light irradiation to activate the impurity injected into thesource region S and the drain region D.

The process goes to the step shown in FIG. 13L, and contact holes areopened in the first inter-layer insulating film 6. After that, aluminumis stacked to the thickness of 600 nm by sputtering, and patterned intoa predetermined configuration to form the wiring electrode 7. Theprocess goes forth to the step shown in FIG. 13C, and PSG, for example,is stacked to form a second inter-layer insulating film 8 so as to coverthe wiring electrode 7. Then the process moves to the step shown in FIG.13N, and Ti is stacked on the second inter-layer insulating film 8 bysputtering to use it as a shade film 9. The process moves to the stepshown in FIG. 130 in which heat of 400° C. is applied for 90 minutes ina forming gas atmosphere to diffuse hydrogen contained in the secondinter-layer insulating film 8 into the semiconductor thin film 2. Byso-called hydrogenation, the operation property of the thin filmtransistors are stabilized. The forming gas is nitrogen gas containinghydrogen by about 4%. Through these steps, thin film transistors havingthe top-gate structure are completed. In the case where the thin filmtransistors are used as pixel switching elements, after the shade film 9is patterned into a predetermined configuration, pixel electrodes in theform of an ITO or other transparent conductive film are made inconnection therewith.

Here is given an explanation on lowering the process temperature of thesemiconductor thin film used as the active layer of the thin filmtransistors. Heretofore, plasma CVD has been employed for making asilicon or other semiconductor thin film at a low temperature not higherthan 600° C. Plasma CVD is a method for introducing a source materialgas of monosilane, for example, into a reaction chamber which can beevacuated, and a high frequency wave is applied to decompose the sourcematerial gas into hydrogen and silicon. Then, it stacks the decomposedsilicon on an insulating substrate to form a semiconductor thin film.However, since monosilane does not fully decompose into hydrogen andsilicon, hydrogen atoms partly connected to silicon atoms are taken intothe film, and the hydrogen content in the semiconductor thin film isvery high. Additionally, semiconductor thin films stacked by plasma CVDare usually amorphous. For changing amorphous silicon containing a lotof hydrogen atoms into a polycrystal, laser annealing is used as a partof a low-temperature process. However, since a large amount of hydrogenis contained in the film, when it is heated instantaneously by laserannealing, bumping of hydrogen, for example, occurs, and this remains asa problem in the manufacturing process. Additionally, since plasma CVDbasically relies on a high frequency wave to decompose the sourcematerial gas, it is difficult to uniformly grow the semiconductor thinfilm over the entirety of the substrate having a large area.

Taking into account these drawbacks of plasma CVD, the inventioncombines catalytic CVD and laser annealing to enable fabrication ofhigh-quality polycrystalline semiconductor thin films at low processtemperatures. Explained below is a method for forming a semiconductorthin film according to the invention with reference to FIG. 14. As shownin FIG. 14A, the manufacturing apparatus used for this method has astructure incorporating the laser anneal apparatus shown in FIG. 2 andthe catalytic CVD apparatus shown in FIG. 10. The invention, however, isnot limited to this example, and separate catalytic CVD apparatus andlaser anneal apparatus may be used sequentially to fabricate thesemiconductor thin film. This manufacturing apparatus is assembled byusing a reaction chamber 71 which can be evacuated, and includes a stage55 and a drive mechanism 57 for driving it right and left; both of whichare disposed on its bottom. The stage 55 supports thereon an insulatingsubstrate 1 in the form of a glass plate, for example. In FIG. 14A, thestage 55 is located on the left side, and the semiconductor thin film isformed by catalytic CVD. At the top of the reaction chamber 71, a sourcematerial supply tube 74 is mounted. A flat-shaped nozzle 742 is attachedto one end of the source material supply tube 74 inserted into thereaction chamber 71. The nozzle 742 has a gas dispersion plate 741inside. A source material gas introduced through the supply pipe 74 issprayed into the reaction chamber 71 by the nozzle 742. At the position4 through 5 cm higher than the substrate 1 between the nozzle 742 andthe stage 55, a catalytic body 73 is placed. The catalytic body 73 is acoil-shaped winding of tungsten wire, for example, and it is heated to1600 through 1800° C., for example. The reaction chamber 71 is evacuatedto form a pressure-reduced condition, and the insulating substrate 1 isheated to 300 through 400° C. by a heater contained in the stage 55. Thesource material gas sprayed out of the nozzle 742 catalyticallydecomposes at the surface of the catalytic body 73, and a film stacks onthe insulating substrate 1. Used as the source material gas is a mixtureof monosilane and hydrogen or monosilane as simple substance. In thecatalytic CVD, since the source material gas itself is decomposedsubstantially completely by the catalytic body 73 at a very hightemperature while maintaining the insulating substrate 1 at a lowtemperature not higher than 400° C., the stacked film has a densepolycrystalline property, and contains hydrogen as small as 1% or less.

As shown in FIG. 14B, when deposition of the semiconductor thin film bycatalytic CVD is finished, the stage 55 is moved from the left side tothe right side in the reaction chamber 71 by a drive mechanism 57 whileholding the insulating substrate 1 thereon. In this process, since theevacuated condition of the reaction chamber 71 is not broken, it isadvantageous for efficiency of the manufacturing process. Special glass501 transparent to ultraviolet rays is put on the top of the reactionchamber 71, and a laser anneal apparatus 500 as shown in FIG. 2 ismounted thereon. The laser anneal apparatus 500 includes an excimerlaser source which intermittently emits laser light 50 whose pulse widthis not shorter than 100 ns to improve the quality of the semiconductorthin film 2 of polycrystalline silicon formed on the insulatingsubstrate 1. The laser light 50 is shaped to form a rectangular crosssection, and it is irradiated step by step onto the semiconductor thinfilm 2. The stage 55 is movable in the XY directions. By driving thestage 55, laser light 50 is moved step by step relative to thesemiconductor thin film 2 so that the rectangular cross section partlyoverlaps, and sequentially irradiates its surface. As a result, it ispossible to remove defects contained in the crystal grains and obtainhigh-quality polycrystalline silicon. In this process, by irradiatingthe laser light 50 with an energy not inviting destruction of crystalgrains, defects in the crystal grains can be removed, and the quality ofthe semiconductor thin film 2 can be improved. When the improvedsemiconductor thin film 2 is used as the active layer of thin filmtransistors, thickness of the semiconductor thin film 2 is preferably 50nm or less.

Depending on circumstances, semiconductor thin films 2 can be stackeduntil reaching a desired thickness by alternately repeating catalyticCVD and laser annealing. For example, by stacking a semiconductor thinfilm 2 having a thickness around 10 nm in one catalytic CVD andrepeating it five times, the semiconductor thin film 2 having thethickness of 50 nm can be formed. In this method, since semiconductorthin films are sequentially stacked over the surface of another alreadyimproved by laser annealing, good crystal grains grow on the improvedbase film as the core. Additionally, according to the invention, bycombining chemical vapor deposition using a catalyst with laserannealing, it is possible to efficiently make high-quality semiconductorthin films in a low-temperature process.

With reference to FIG. 15,a thin film transistor manufacturing methoddealing with the third object of the invention is explained below indetail. First as shown in FIG. 15A, two base films 16 a and 16 b to beused as a buffer layer are consecutively formed on the insulatingsubstrate 1 by plasma CVD. The base film 16 a as the first layer is madeof SiN_(x) and its thickness is 100 through 200 nm. The base film 16 bas the second layer is made of SiO₂, and its thickness is also 100 nmthrough 200 nm. On the base film 16 b of SiO₂, a semiconductor thin film2 of polycrystalline silicon is formed to a thickness in the range of 40through 100 nm by low pressure chemical vapor deposition (LP-CVD).Consecutively, Si⁺ ions are injected into the semiconductor thin film 2under acceleration by an electric field by an ion implantationapparatus, for example, to change the polycrystalline silicon toamorphous phase. Instead of the method for first stacking thepolycrystalline silicon and then changing it to amorphous phase, it ispossible to originally stack a semiconductor thin film 2 of amorphoussilicon on the insulating substrate 1 by low pressure chemical vapordeposition (LP-CVD), plasma CVD or sputtering, for example. After that,solid phase growth is conducted by annealing the semiconductor thin film2 of amorphous silicon at 630° C. for about 12 hours in a nitrogenatmosphere. In this process, the semiconductor thin film 2 ispolycrystalline, and grain size of the polycrystalline silicon grows toabout 1 μm. By using catalytic CVD instead of solid phase growth, thesemiconductor thin film 2 containing polycrystalline grains may beformed directly by using the CVD apparatus shown in FIG. 10.

After that, using the laser anneal apparatus shown in FIG. 2, pulse-modelaser light 50 having an emission time not shorter than 50 ns isirradiated onto the semiconductor thin film 2 to remove residual defectsfrom the crystal grains and further enlarge the crystal grains. Thisembodiment not only remedies crystal defects contained in thepolycrystalline semiconductor thin film 2 by using the laser annealapparatus having a large-power excimer laser source, but also increasesthe crystal grains still further, and therefore largely contributes toimprovement of the mobility of thin film transistors. In the laserannealing step, irradiation of pulse-mode laser light 50 can be repeatedover a number of times necessary for enlarging the crystal grains to adesired size. In the laser annealing step, pulse-mode laser light isirradiated cyclically with the period of ⅙ Hz for the purpose ofshortening the throughput. The high-power laser anneal apparatus shownin FIG. 2 has the power of pulse-mode emission of the laser light withthe period of ⅙ Hz or higher. In the laser annealing step, the laserlight is irradiated onto the semiconductor thin film with the energydensity of 400 through 600 mJ/cm². This range of energy density makes itrealize remedy of crystal defects and enlargement of crystal grains.Although the laser anneal apparatus shown in FIG. 2 has a high outputpower capable of emitting pulse-mode laser light basically having theemission time of 50 ns or more, preferably by using pulse-mode laserlight having an emission time not shorter than 100 ns, remedy of crystaldefects and enlargement of crystal grains are done efficiently. Thislaser anneal apparatus has a large output power and can irradiate laserlight having an irradiation area of 5 cm² or more onto the semiconductorthin film 2 each time. So, the throughput has been improved as comparedwith conventional apparatuses.

After that, as shown in FIG. 15B, the semiconductor thin film 2 made ofpolycrystalline silicon, which is remedied in crystal defects andenlarged in crystal grain size, is patterned in the form of islands.Grown thereon is SiO₂ up to 50 through 400 nm by plasma CVD, normalpressure CVD, low pressure CVD, ECR-CVD or sputtering, for example, toform a gate insulating film 4. If necessary, V_(th) ion implantation maybe done to inject B⁺ ions into the semiconductor thin film 2 by a doseamount in the level of 0.5×10¹² through 4×10¹²/cm², for example. In thiscase, acceleration voltage is about 80 keV. This V_(th) ion implantationmay be done before the gate insulating film 4 is formed. After that, Al,Ti, Mo, W, Ta, doped polycrystalline silicon, or an alloy of any ofthese materials is deposited on the gate insulating film 4 up to athickness of 200 through 800 nm, and it is patterned into apredetermined configuration to form the gate electrode 5. Subsequently,P⁺ ions are injected into the semiconductor thin film 2 by ionimplantation using mass separation to form an LDD region. This ionimplantation is done over the entire surface of the insulating substrate1, using the gate electrode 5 as a mask. The dose amount is 6×10¹²through 5×10¹³/cm². The channel region Ch located immediately below thegate electrode 5 is protected, and B⁺ ions previously injected by V_(th)ion implantation are maintained there. After ion implantation to the LDDregion, a resist pattern is formed to cover the gate electrode 5 and itssurrounding area, and P⁺ ions are injected to a high concentration byion shower doing of a mass non-separation type to form the source regionS and the drain region D. In this case, the dose amount is about1×10¹⁵/cm², for example. For formation of the source region S and thedrain region D, a mass separation type ion implantation apparatus may beused. After that, the dopant injected into the semiconductor thin film 2is activated. This activation process may be done by laser annealing.

Finally, as shown in FIG. 15C, an inter-layer insulating film 6 of PSG,for example, is stacked to cover the gate electrode 5. After somecontact holes are opened in the inter-layer insulating film 6, Al-Si,for example, is stacked by sputtering, and then patterned into apredetermined configuration to form the wiring electrode 7. Then,SiN_(x) is stacked as a passivation film (cap layer) 8 to about 200through 400 nm by plasma CVD so as to cover the wiring electrode 7. Inthis stage, so-called hydrogenation is conducted to improve the propertyof thin film transistors, which includes annealing in nitrogen gas atthe temperature of 350° C. for one hour and diffusion of hydrogencontained in the inter-layer insulating film 6 into the semiconductorthin film 2. After a smoothing layer 10 of acrylic resin, for example,is coated on the passivation film 8 to a thickness around 1 μm, contactholes are opened therethrough. Then, a transparent conductive film ofITO or IXO is stacked on the smoothing layer 10 by sputtering, andpatterned into a predetermined configuration to form the pixelelectrodes 11.

FIG. 16 is a graph showing the relation between the repeated number ofirradiation (number of shots) of pulse-mode laser light and the grainsize of crystal grains contained in the polycrystalline semiconductorthin film 2. The data shown in FIG. 16 is a measured value, and laserlight having a cross-sectional area not smaller than 5 cm² is irradiatedin the form of pulses with the period of ⅙ Hz by using an excimer lasersource. Emission time (pulse width) of the laser light is set in 200 ns.As apparent from the graph, by repeatedly irradiating pulse-mode laserlight 5 to 20 times, crystal grains exceed 1 μm and reach 2 μm. Theirradiation frequency of laser light had better be larger, and longeremission time give a better result. In general, the optimum number ofirradiation (number of shots) varies with frequency and emission time.

FIG. 17 contains measured data demonstrating the relation between thenumber of shots and the mobility of thin film transistors. As apparentfrom the graph, as the number of shots increases, the crystal grain sizeincreases, and it results in improving the mobility of the thin filmtransistors. For example, when the number of shots n is 20, the mobilityof the n-channel thin film transistors reaches 200 cm²/V·s.

FIG. 18 is a graph showing the relation between the irradiation energydensity of laser light and the mobility of n-channel thin filmtransistors. The belt-like portion in the graph indicates the mobilityof thin film transistors including polycrystalline silicon formed bytypical solid phase growth as their active layer, and it is in the rangefrom 80 to 100 cm²/V·s, approximately. In contrast, in the presentinvention, by setting the irradiation energy density per each shot ofexcimer laser light to 400 through 600 mJ/cm², a higher mobility thanconventional ones can be obtained. By repeating this, the mobility canbe increased to about 200 cm²/V·s as shown in FIG. 18.

As explained above, according to an aspect of the invention, by usingexcimer laser light whose pulse width is not shorter than 50 ns andshaping the beam size to 10 mm×10 mm or more, for example, the excimerlaser light is irradiated while being moved step by step so that thereis produced a portion on the semiconductor thin film preferably made ofamorphous silicon, which is irradiated at least twice. By choosing anappropriate number of shots according to the specification of the activematrix display device to be manufactured, polycrystalline silicon havingcrystal grain sizes and uniformity meeting the requirement can be builtin over the entire surface of the substrate. As a result, a high-qualityactive matrix display device can be manufactured. Especially, it ispossible to manufacture a so-called system-on-panel with an additionalvalue, which contains all peripheral circuits like a video driver and atiming generator in addition to scanners inside the panel. So, itseffect is great.

According to the second aspect of the invention, by using pulse-modelaser light having an emission time not shorter than 100 nm andirradiating the semiconductor thin film with an energy not invitingdestruction of crystal grains, residual defects are removed from crystalgrains. As a result of this process, it is possible to make asemiconductor thin film made of polycrystalline silicon having lesscrystal defects and larger grain sizes. So, it contributes to increasingthe mobility of thin film transistors. Additionally, if a mobilityequivalent to conventional ones is acceptable, the time for solid phasegrowth of the polycrystalline semiconductor thin film can be shortened,thereby improving productivity. Furthermore, according to the invention,by combining chemical vapor deposition using a catalyst with laserannealing, it is possible to efficiently make a high-qualitypolycrystalline semiconductor thin film in a low-temperature process.

Moreover, according to the third aspect of the invention, sincepulse-mode laser light having an emission time not shorter than 50 ns isirradiated onto the semiconductor thin film to not only remove residualdefects from crystal grains but also enlarge the crystal grains, apolycrystalline silicon thin film having less crystal defects and largergrain sizes can be formed on the insulating substrate, and thin filmtransistors having a high mobility can be obtained. It is thereforepossible to manufacture display devices, etc. having a large additionalvalue, which contains built-in peripheral circuits in the panel.Additionally, since any mobility necessary for a target system like adisplay device, etc. can be selected by adjusting the number of shots ofirradiation, devices not requiring a very high mobility can bemanufactured with a high throughput in the same manufacturing line asthat of devices required to have a high mobility.

What is claimed is:
 1. A method for manufacturing a thin filmsemiconductor device comprising: a film-making step for forming asemiconductor thin film of a non-single crystal on one surface of aninsulating substrate; and an annealing step for irradiating laser lightand changing-said semiconductor thin film of the non-single crystal intoa polycrystal, said annealing step irradiating laser light with a pulsewidth not shorter than 50 ns onto said semiconductor thin film by usingan excimer laser source, wherein said annealing step shaped the laserlight to have a rectangular cross-sectional area whose each side is notsmaller than a predetermined dimension, and then sequentially irradiatesthe surface of the semiconductor thin film while moving laser light stepby step so that the rectangular cross-sectional areas partly overlapalong their sides.
 2. The method for manufacturing a thin filmsemiconductor device according to claim 1 wherein said annealing stepsets the number of irradiation of laser light per each stepping movementso that the number of irradiation shots of laser light repeated on aparticular portion of the surface of the semiconductor thin film reachesa desired number.
 3. A method for manufacturing a display device whichincludes a pair of substrates bonded to each other via a predeterminedgap and an electrooptic substance held in the gap, transparent one ofthe substrates having formed an opposite electrode, and the otherinsulating substrate having formed a pixel electrode and a thin filmtransistor for driving the pixel electrode, which includes: afilm-making step for making a non-single-crystalline semiconductor thinfilm on one surface of said insulating substrate; an annealing step forirradiating laser light to once heat and melt the non-single-crystallinesemiconductor thin film, and the changing it to a polycrystal in itscooling process; and a processing step for forming in an integrated formsaid thin film transistor including the semiconductor thin film changedinto a polycrystal as its active layer, characterized in that: saidannealing step uses an excimer laser source and irradiates laser lighthaving a pulse width not shorter than 50 ns onto said semiconductor thinfilm.
 4. A method for manufacturing a thin film transistor in which amulti-layered structure including a semiconductor thin film, a gateinsulating film stacked on one surface of the semiconductor thin film,and a gate electrode stacked on the semiconductor thin film via the gateinsulating film is formed on an insulating substrate, comprising: aforming step for forming a semiconductor thin film containingpolycrystalline grains on the insulating substrate; and a laserannealing step for using pulse-mode laser light having an emission timenot shorter than 100 ns and irradiating said semiconductor thin filmwith an energy of a level not inviting destruction of crystal grains toremove residual defects from crystal grains, wherein said laserannealing step irradiates laser light onto said semiconductor thin filmwith an energy not lower than 500 mJ/cm² and not higher than 600 mJ/cm².5. The method for manufacturing a thin film transistor according toclaim 4 wherein said forming step includes a film-making step forstacking on the insulating substrate an amorphous semiconductor thinfilm or a polycrystalline semiconductor thin film including crystalgrains with relatively small grain sizes, and a solid phase growth stepfor annealing said semiconductor thin film to grow crystal grains withrelatively large grain sizes in solid phase.
 6. The method formanufacturing a thin film transistor according to claim 4 wherein saidforming step stacks a semiconductor thin film containing polycrystallinegrains on the insulating substrate by chemical vapor deposition using acatalyst.
 7. A method for manufacturing a thin film transistor in whicha multi-layered structure including a semiconductor thin film, a gateinsulating film stacked on one surface of the semiconductor thin film,and a gate electrode stacked on the semiconductor thin film via the gateinsulating film is formed on an insulating substrate, comprising: afilm-making step for an amorphous semiconductor thin film or apolycrystalline semiconductor thin film made of crystal grains withrelatively small grain sizes on an insulating substrate; a solid phasegrowth step for annealing said semiconductor thin film to grow crystalgrains with relatively large grain sizes in solid phase; a laserannealing step using pulse-mode laser light for irradiating saidsemiconductor thin film with an energy of a level not invitingdestruction of large crystal grains to remove residual defects fromcrystal grains; and an additional solid growth step for again annealingsaid semiconductor thin film to grow crystal grains with still largergrain sizes in solid phase.
 8. The method for manufacturing a thin filmtransistor according to claim 7 further comprising an additional laserannealing step after the additional solid phase growth step to againirradiate said semiconductor thin film with an energy of a level notinviting destruction of large crystal grains by using pulse-mode laserlight and thereby remove defects produced in the additional solid phasegrowth step.
 9. The method for manufacturing a thin film transistoraccording to claim 7 wherein said laser annealing step uses pulse-modelaser light having an emission time not shorter than 100 ns.
 10. Themethod for manufacturing a thin film transistor according to claim 7wherein said laser annealing step irradiates laser light onto saidsemiconductor thin film with an energy not higher than 600 mJ/cm².
 11. Amethod for manufacturing a display device including a pair of substratesbonded to each other via a predetermined gap and an electroopticsubstance held in said gap, one of said substrates having formed anopposite electrode and the other of the substrates having formed a pixelelectrode and a thin film transistor for driving the pixel electrode,and said thin film transistor being made of a semiconductor thin filmand a gate electrode stacked on one surface of the semiconductor thinfilm via a gate insulating film, comprising: a film-making step forstacking on an insulating substrate an amorphous semiconductor thin filmor a polycrystalline semiconductor thin film including made up ofcrystal grains with relatively large grain sizes; a solid phase growthstep for annealing said semiconductor thin film to grow crystal grainswith relatively large grain sizes in solid phase; and a laser annealingstep for irradiating said semiconductor thin film by using pulse-modelaser light having an emission time not shorter than 100 ns with anenergy of a level not inviting destruction of large crystal grains toremove residual defects from crystal grains.
 12. A method formanufacturing a display device including a pair of substrates bonded toeach other via a predetermined gap and an electrooptic substance held insaid gap, one of said substrates having formed an opposite electrode andthe other of the substrates having formed a pixel electrode and a thinfilm transistor for driving the pixel electrode, and said thin filmtransistor being made of a semiconductor thin film and a gate electrodestacked on one surface of the semiconductor thin film via a gateinsulating film, comprising: a film-making step for stacking on aninsulating substrate an amorphous semiconductor thin film or apolycrystalline semiconductor thin film including made up of crystalgrains with relatively large grain sizes; a solid phase growth step forannealing said semiconductor thin film to grow crystal grains withrelatively large grain sizes in solid phase; a laser annealing step forirradiating said semiconductor thin film by using pulse-mode laser lightwith an energy of a level not inviting destruction of large crystalgrains to remove residual defects from crystal grains; and an additionalsolid phase growth step for again annealing said semiconductor thin filmto grow crystal grains with still larger grain sizes in solid phase. 13.The method for manufacturing a display device according to claim 12further comprising an additional laser annealing step after theadditional solid phase growth step to again irradiate said semiconductorthin film by using pulse-mode laser light with an energy of a level notinviting destruction of large crystal grains to remove defects producedin the additional solid phase growth step.
 14. A method for making asemiconductor thin film comprising: a forming step for making asemiconductor thin film on an insulating substrate at a temperature nothigher than 400° C. by chemical vapor deposition using a catalyst; and alaser annealing step for irradiating pulse-mode laser light having anemission time not shorter than 100 ns onto the insulating substrate toimprove the quality of said semiconductor thin film.
 15. The method formaking a semiconductor thin film according to claim 14 wherein saidforming step makes a polycrystalline semiconductor thin film containingcrystal grains by chemical vapor deposition using a catalyst, and saidlaser annealing step irradiates laser light with an energy of a levelnot inviting destruction of said crystal grains to remove defectsexisting in said crystal grains.
 16. The method for making asemiconductor thin film according to claim 14 wherein said forming stepmakes on the insulating substrate a semiconductor thin film having ahydrogen content not higher than 1% and a thickness not larger than 50nm by chemical vapor deposition using a catalyst.
 17. The method formaking a semiconductor thin film according to claim 14 wherein saidforming step makes a semiconductor thin film on the insulating substratein a reaction chamber which can be evacuated, and said laser annealingstep irradiates laser light onto the insulating substrate withoutbreaking the evacuated condition of the reaction chamber.
 18. The methodfor making a semiconductor thin film according to claim 14 wherein saidforming step and said laser annealing step are alternately repeateduntil said semiconductor thin film is stacked to a desired thickness.19. A method for manufacturing a thin film transistor in which amulti-layered structure including a semiconductor thin film, a gateinsulating film stacked on one surface of the semiconductor thin film,and a gate electrode stacked on the semiconductor thin film via the gateinsulating film is formed on an insulating substrate, comprising: aforming step for making a semiconductor thin film containing,polycrystalline grains on the insulating substrate; and a laserannealing step for irradiating pulse-mode laser light having an emissiontime not shorter than 50 ns onto said semiconductor thin film to removeresidual defects from crystal grains and enlarge the crystal grains,wherein said laser annealing step repeats irradiation of pulse-modelaser light certain times necessary to enlarge the crystal grains to adesired size.
 20. The method for manufacturing a thin film transistoraccording to claim 19 wherein said laser annealing step repeatedlyirradiates pulse-mode laser light with the period not lower than ⅙ Hz.21. The method for manufacturing a thin film transistor according toclaim 19 wherein said laser annealing step irradiates laser light ontosaid semiconductor thin film with an energy density not lower than 400mJ/cm² and not higher than 600 mJ/cm².
 22. The method for manufacturinga thin film transistor according to claim 19 wherein said laserannealing step uses pulse-mode laser light having an emission time notshorter than 100 ns.
 23. The method for manufacturing a thin filmtransistor according to claim 19 wherein said laser annealing stepirradiates laser light having an irradiation area not smaller than 5 cm²onto said semiconductor thin film.
 24. The method for manufacturing athin film transistor according to claim 19 wherein said forming stepincludes a film-making step for stacking an amorphous semiconductor thinfilm or a polycrystalline semiconductor thin film made up of crystalgrains with relatively small grain sizes on an insulating substrate, anda solid phase growth step for annealing said semiconductor thin film togrow crystal grains with relative large grain sizes in solid phase. 25.The method for manufacturing a thin film transistor according to claim19 wherein said forming step stacks a semiconductor thin film containingpolycrystalline grains on the insulating substrate by chemical vapordeposition using a catalyst.